Riveting members are known which are essentially comprised of two pieces: a mandrel having a shank and a head, and a tubular sleeve intended to receive the shank of the mandrel and to be deformed by its head in order to constitute a post-formed fastening head on one side of the materials. For example, reference is had to French patent 2,306,361 which describes a riveting member of this type. However, known members of this type are not suited to brittle or fragile materials: in effect, during riveting, the sleeve undergoes at its end a sizeable radial expansion (for creating the post-formed head), susceptible of seriously damaging this type of materials in the area situated beneath said post-formed head, with risks of delamination and unbonding of the fibers. In addition, regardless of the materials assembled, the fastening range created by the post-formed head has a generally longitudinal direction and is of reduced dimensions such that the fastening hold is mediocre.
In addition, the document EP-A-0.216.405 describes in reference to its FIGS. 7 to 10, a blind riveting process, that is a process of riveting in which the access is available from only one side of the materials to be riveted, and which is achieved by a rupturing of the mandrel due to an appropriate tensile force exerted thereon. This process avoids damaging the materials at the level of the postformed head but it is subject to the drawbacks of blind processes (in particular to those related to the need to break the shank of the mandrel at the completion of the riveting), and leads to an assembly with reduced strength. Moreover, this process does not permit in any case introducing radial compressire forces between the sleeve and the materials to be riveted without damaging the latter. In many applications, these compressive forces are desired for increasing the fatigue strength of the assembly.
The present invention seeks to provide a new riveting process which can be used for all materials without risk of damage in the case of fragile materials, and which leads to an excellent fastening behavior (shear, tensile, fatigue strength).
Another object of the invention is to permit production of a countersunk/countersunk assembly, with a good flattening, without having to carry out a separate flattening step on the riveting member.